1. Field of Inventions
The present inventions relate to novel hard, non-toxic, substantially non-hydrophilic artificial dentures including dentures comprising teeth anchored in or bonded to the denture material; to novel non-toxic, non-hydrophilic dentures containing teeth anchored in a gum member comprising a tooth holding portion and a mouth engaging portion, the tooth-holding portion of which comprises rigid material described hereinafter and the mouth engaging portion of which comprises soft elastomeric material described hereinafter; to novel processes for fabricating the aforesaid dentures; and to novel mixtures or systems, generally two package systems, particularly those utilized in the preparation of the said rigid material of the tooth-holding portion of the denture.
2. Prior Art
Conventional hard prosthetic dentures have in the past been manufactured by setting individual teeth in a hard base structure formed from suitable plastics such as various hard acrylic resins. Such dentures may be made by making an initial impression in a suitable soft material such as alginate. The initial impression is then used to form a custom tray. The tray, in turn, is then used to make a secondary impression from polysulfide rubber or other similar material. The final steps involve forming the denture in wax, investing, and lost wax techniques. The denture is then fitted to the wearer and suitably lined to conform to the wearer's edentulous ridge.
Conventional hard dentures have also been provided with a soft layer to provide tissue relief. Such soft layers may be composed of acrylics, silicones and other rubber-like materials. U.S. Pat. Nos. 4,024,636, 4,024,637 and 4,080,412 to Colpitts and Frisch state that such soft layers, on aging, tend to harden and give off undesirable odors. Additionally, the patentees, Colpitts and Frisch, point out that some decomposition of the soft layer material may also occur presumably due to an oxidation process as well as pH fluctuations within the mouth. These patentees therefore propose an inexpensive, trouble-free, and easy to keep clean denture which they state overcomes the difficulties heretofore encountered in the prior art by providing for dentures consisting essentially of a hard portion (tooth holding portion) of non-hydrophilic polyether polyurethane having a hardness of not less than Shore D 40 and a soft portion (mouth-engaging portion) of non-hydrophilic polyether polyurethane having a hardness of not greater than Shore A 65.
U.S. Pat. No. 4,225,696 issued Sept. 30, 1980 to Colpitts and Wendt discloses that the hard non-hydrophilic polyurethane member of the dentures of the above-mentioned U.S. Pat. Nos. 4,024,636, 4,080,412 and 4,024,637 are "susceptible to distortion under the conditions prevailing in the mouth. Such distortion, accompanied by a loss of dimensional stability of the dentures, interferes with the ability of the dentures to retain a good fit with the mouth and remain in place without slippage;" column 1, lines 51-56 of U.S. Pat. No. 4,225,696. Under the "Summary of the Inventions" in column 1 and 2 thereof, the patentees state:
"It has now been discovered that polyurethane elastomers for use in artificial dentures can be provided with enhanced resistance to thermal distortion under the conditions of use when prepared from a polyether polyol and an aromatic polyisocyanate which the isocyanate groups are bonded directly to the aromatic nucleus and not to an aliphatic group as in the polyisocyantes employed in the preparation of known polyurethane elastomer dentures. As a result of the excellent degree of resistance to thermal distortion, dentures made with the aromatic polyisocyanate-based hard polyurethane elastomers herein retain a close fit with the mouth and are virtually free of any tendency toward slippage to which dentures made with prior polyurethane resins are liable. PA1 Thus, in accordance with the present invention, a prosthetic denture is provided which is fabricated with a hard, substantially non-hydrophilic polyurethane elastomer with a hardness of not less than about Shore D 60 and preferably not greater than about Shore D 100, the elastomer being prepared from the reaction of a polyether polyol and an aromatic polyisocyanate in which the isocyanate groups are bonded directly to the aromatic nucleus. PA1 While the hard polyurethane elastomer can be used in the preparation of the entire denture, including the teeth if so desired, it is also within the scope of this invention to utilize the hard polyurethane elastomer as the tooth-engaging portion of the denture bonded to a soft, substantially non-hydrophilic elastomer employed as the mouth-engaging portion of the denture. The latter elastomer can be selected from among any of the soft resins heretofore known and/or used in dental prostheses including the soft non-hydrophilic polyurethane elastomers of U.S. Pat. Nos. 4,024,636 and 4,080,412 to Colpitts et al, supra, which have a hardness of not greater than about Shore A 65 and preferably not less than about Shore A 15. Advantageously, the soft resin is a polyurethane prepared with a polyether polyol and an aromatic polyisocyanate in which the isocyanate groups are bonded directly to the aromatic nucleus. Accordingly, the invention herein further comprises a denture in which hard polyurethane elastomer and soft polyurethane elastomer elements as aforedescribed are bonded to form a unitary whole."